Diacetoxyalkenes are intermediates used in making alkanediols which are themselves useful products. One such product, 1,4-butanediol, is a raw material in producing tetrahydrofuran (a known solvent) and a relatively new engineering plastic, polybutylene terephthalate.
Several methods are known to produce 1,4-butanediol. One such method is disclosed in U.S. Pat. No. 4,164,616, issued Aug. 14, 1979, wherein 1,4-butanediol is prepared in a 4-step continuous process by: (1) reacting butadiene and bromine to form 1,4-dibromo-2-butene which is almost instantaneously reacted with potassium acetate to form 1,4-diacetoxy-2-butene; (2) hydrogenating the double bond; (3) hydrolyzing to the corresponding diol; and (4) electrolyzing the alkali metal halide by-product to liberate free bromine and alkali metal hydroxide which are then returned for use in the process. Basically, this invention is an improvement in step 2 of the above-mentioned process.
It is known that various additives when present during the hydrogenation of 1,4-diacetoxy-2-butene enhance the conversion to 1,4-diacetoxybutane. For example, U.S. Pat. No. 4,117,242 discloses the use of monoamines such as triethylamine during the hydrogenation of 1,4-diacetoxy-2-butene to 1,4-diacetoxybutane in the presence of a palladium catalyst. Likewise, U.S. Pat. No. 3,919,294 discloses the use of zinc or vanadium in the presence of a nickel catalyst during the same hydrogenation reaction.
U.S. Pat. No. 3,872,163 discloses a catalyst system comprised of palladium on alumina or charcoal and an alkali metal salt of a carboxylic acid such as potassium acetate. However, the catalyst is employed in an oxidation reaction wherein a conjugated diene such as butadiene is reacted with oxygen and acetic acid to give a mixture of 1,4-diacetoxy-2-butene and 1,2-diacetoxy-3-butene. Hydrogenation of these products with the same catalyst is not mentioned.
The disclosures of the patents mentioned herein are incorporated by this reference to them.
It is an object of this invention to produce a diacyloxy saturated hydrocarbon. It is another object of this invention to provide an improved process for the hydrogenation of a diacyloxyolefin. It is a further object of this invention to convert 1,4-diacetoxy-2-butene to 1,4-diacetoxybutane. It is a further object of the invention to improve the hydrogenation effected thereby to avoid the formation of undue amounts of by-product, e.g., butyl acetate as when 1,4-diacetoxy-2-butene is hydrogenated to produce 1,4-diacetoxybutane.
Other aspects, concepts, objects and the several advantages of the invention are apparent from a study of this disclosure and the appended claims.
According to the present invention, a diacyloxyolefin is converted by hydrogenation in the presence of at least one of an alkali and an alkaline earth metal salt of a carboxylic acid.